(Bloomberg) -- Thailand will hold a general election on May 14, with a pre-poll survey showing opposition parties holding a clear lead over military-backed establishment parties in the outgoing government led by Prime Minister Prayuth Chan-Ocha.

Candidates should register to contest the 400 constituency seats to the House of Representatives from April 3 to April 7, the Election Commission said Tuesday. Political parties will need to nominate their candidates for the party-list seats from April 4 to 7, it said in a statement.

Parties must submit a list of their prime ministerial nominees to the election agency by April 7. After the May vote, the newly-elected members of the lower house and the military-appointed Senate will pick Thailand’s next leader from the list of candidates.

The setting of the election date follows the dissolution of the House of Representatives on Monday, days before it was due to complete its four-year term.

A survey published on March 19 showed Prayuth, 69, falling to the third position in the ranking of preferred prime minister candidates, as opposition Pheu Thai Party’s Paetongtarn Shinawatra, daughter of ousted former premier Thaksin Shinawatra, widened her lead as the top choice. 

Pheu Thai, which is bidding to win more than 300 seats, had 49.8% approval rating among voters in the quarterly survey by the National Institute of Development Administration. It was followed by liberal Move Forward party at 17.4% and Prayuth’s United Thai Nation party in the third spot with a backing of 11.8%.

Although pre-election surveys project opposition parties holding an edge, the rules are stacked in favor of military-backed groups. That’s because the 2017 constitution gives the 250-member Senate, comprising mostly of establishment allies, the power to vote alongside the lower house until 2024 to pick the next prime minister.

The new leader must win the backing of at least 376 lawmakers and Senators, or more than half of the combined houses.

“The 2017 constitution has separated the election from the government formation,” said Yuttaporn Issarachai, political scientist at Sukhothai Thammathirat Open University. “People’s votes don’t guarantee the government will reflect what they want. The government formation game will involve the Senate in the prime ministerial pick. Pheu Thai’s victory won’t necessarily mean it will get to form the government.”

Thaksin-linked parties have won the most seats in every election since 2001, only to be unseated from government by the army or the courts. The party is rooted in poor, rural regions in the north and northeast and has long riled Thailand’s urban establishment and royalist elite.

The May election will be the first since 2019 when Palang Pracharath Party, formed by allies of Prayuth’s then-military junta, won the most votes and cobbled together a coalition to allow him to retain the top job. The former army chief, who has been in power since the 2014 coup that toppled a government headed by Thaksin’s sister Yingluck Shinawatra, is now seeking to extend his rule with the newly-formed United Thai Nation.

Prayuth is betting the return of millions of tourists and billions of dollars in stimulus programs will boost Southeast Asia’s second largest economy and his election prospects. However, he’s facing voter discontent arising from high living costs and an uneven economic recovery.

More than 52 million voters will elect 500 members to the lower house in a return to the two-ballot system that will see 100 seats being alloted based on the proportion of votes that each party receives. 

While the preliminary outcome of the vote will be available on the same night, official results may take about two months and will likely be announced sometime in early July, according to government spokesman Anucha Burapachaisri.

That will allow the next parliament to hold its first meeting in mid-July and the selection of the next prime minister will likely take place at the end of that month, according to Anucha.

--With assistance from Cecilia Yap.

(Updates with comment from analyst in ninth paragraph.)

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